since it's already trimmed, I'm not sure there's anything you can do, however, if it's all the corners, it will look like a design element. I would tell her, if she is close by, I would bring the quilt to explain the issue. I don't know if UK long arm quilters normally trim the quilt when it's done, but the quilters I've dealt with here do not normally trim if they do, it's an additional charge agreed to in advance.
If you have her quilt for you in the future, make sure you tell her not to trim!